Low-vibration angle grinders

7/27/2019 Low-vibration angle grinders

1/3

International Journal of Science and Research (IJSR), India Online ISSN: 2319-7064

Volume 2 Issue 6, June 2013www.ijsr.net

Low Vibration Angle GrindersRamesh Kumar Yadav 1, Pankaj Kumar Pal 2, Rohit Choudhary 3

1, 2, 3 Department of Mechanical Engineering, Bhagwant University, Ajmer, Rajasthan- 305004, India

Abstract: Grinding is the process of removing metal by the application of abrasives which are bonded to form a rotating wheel. When the moving abrasive particles contact the work piece, they act as tiny cutting tools, each particle cutting a tiny chip from the work piece. It is a common error to believe that grinding abrasive wheels remove material by a rubbing action; actually, the process is as much a cutting action as drilling, milling, and lathe turning.

Keywords: Grinding machine, metal work piece, wheel

1. Introduction

Efficient grinding depends primarily upon the proper setupof the machine being used. If the machine is not securelymounted, vibration will result, causing the grinder to

produce an irregular surface.[1],[2] Improper alignment

affects grinding accuracy, and it is good practice to check the security and plumb of the machine every few months. Itis advisable to place a strip of cushioning material under themounting flanges, along with any necessary aligning shims,to help absorb vibration.

When a grinding wheel is functioning properly, the abrasivegrains cut very small chips from the work piece and at thesame time a portion of the bond of the wheel is worn away.As long as the bond is being worn away as fast as theabrasive grains of the wheel become dull, the wheel willcontinue to work well. If the bond is worn away too rapidly,the wheel is too soft and will not last as long as it should. If the cutting grains wear down faster than the bond, the faceof the wheel becomes glazed and the wheel will not cutfreely.

2. Classes of Grinding

Precision and semi precision grinding may be divided intothe following classes:

2.1 Cylindrical Grinding

Cylindrical grinding denotes the grinding of a cylindricalsurface. Usually, Cylindrical grinding refers to externalcylindrical grinding and the term internal grinding is used for internal cylindrical grinding. Another form of cylindricalgrinding is conical grinding or grinding tapered work

pieces.

2.2 Tool and Cutter Grinding

Tool and cutter grinding is the generally complex operationof forming and re-sharpening the cutting edges of tool and cutter bits, gages, milling cutters, reamers, and so forth. Thegrinding wheel for any grinding operation should becarefully chosen and the work piece set up properly in thegrinding machine grinding speeds and feeds should beselected for the particular job. Whenever practical, a coolantshould be applied to the point of contact of the wheel and the work piece to keep the wheel and work piece cool, towash away the loose abrasive, and to produce a better finish.

2.3 Material Being Ground

The material being ground will generally determine thegrain, grade, structure, and bond of wheel to be selected.[5]For example, if the wheel is too soft for the material beingcut, an increase in speed will make the wheel act harder.

Conversely, if the wheel is too hard, as lower speed willmake the wheel act softer.

2.4 Type of Grinding Wheel

The type of grinding wheel employed for a particular operation is one of the major considerations in the proper selection of cutting speed. In general practice, the wheelwill be selected for the material to be cut. Therecommended cutting speed can then be determined by thewheel type, bond, and grade of hardness

2.5 Calculating Wheel Size or Speeds

Both cutting speeds in SFPM and rotational speed in RPMmust be known to determine the size wheel to be used on afixed-speed grinding machine. To determine the grindingwheel size, use the following formula:

D = 12 x SDFPM RPM

Where SFPM = Cutting speed of wheel (In surface feet per minute).RPM = Revolutions per minute of wheel.D = The calculated wheel diameter (in inches).

To obtain the cutting speed in SFPM when the wheeldiameter and RPM are given, use the same formula in amodified form:

SFPM = D x RPM 12

To obtain the rotational speed in RPM when the wheeldiameter and desired cutting speed are known use theformula in another modified form:

RPM = 12 SFPM D

3. Work Speed for Cylindrical Grinding

In cylindrical grinding, it is difficult to recommend anywork speeds since these are dependent upon whether the

382


2/3



material is rigid enough to hold its shape, whether thediameter of the work piece is large or small, and so forth.Listed below are areas to consider when performingcylindrical grinding .The larger the diameter of the work

piece, the greater is its arc of contact with the wheel. Thecutting speed suitable for one diameter of work piece might

be unsuitable for another. The highest work speed that themachine and wheel will stand should be used for roughing

The following cylindrical work speeds are only typical: steelshafts, 50 to 55 FPM; hard steel rolls, 80 to 85 FPM; chilled iron rolls, 80 to 200 FPM; cast iron pistons, 150 to 400FPM; crankshaft bearings, 45 to 50 FPM; and crankshaft

pins, 35 to 40 FPM. Higher work speeds increase the cuttingaction of the wheel and may indicate that a harder wheeland a smaller depth of cut be used to reduce wheel wear.

4. Work Speed for Surface Grinding Surface grinding machines usually have fixed work speedsof approximately 50 SFPM or have variable work speed ranges between 0 and 80 SFPM. As with cylindricalgrinding, the higher work speeds mean that more material is

being cut per surface foot of wheel rotation and thereforemore wear is liable to occur on the wheel.

5. Coolants

Most grinding machines are equipped with coolant systems.The coolant is directed over the point of contact between thegrinding wheel and the work. This prevents distortion of thework piece due to uneven temperatures caused by thecutting action. In addition, coolant keeps the chips washed away from the grinding wheel and point of contact, thus

permitting free cutting.

6. Polishing, Buffing and Lapping

Polishing, buffing, and lapping are three closely related methods for finishing metal parts. The three differentmethods of finishing are listed below.

6.1 Polishing

Polishing is an abrading process in which small amounts of metal are removed to produce a smooth or glossy surface byapplication of cushion wheels impregnated or coated with

abrasives.[6] Polishing may be used for reduction or smoothing of the surface to a common level for high finishwhere accuracy is not important or it may be employed for removing relatively large amounts of material from parts of irregular contour. Rough polishing is performed on a drywheel using abrasives of No. 60 grain (60 grains per linear inch) or coarser. Dry finish polishing is a similar processwhere No 70. Grains to No. 120 grain abrasives are used.Oiling is the term applied to polishing with abrasive finer than No. 120 grain. In this process, the abrasive is usuallygreased with tallow or a similar substance.

6.2 Buffing

Buffing is a smoothing operation which is accomplished more by plastic flow of the metal than by abrading. Theabrasives are generally finer than those used in polishing

and instead of being firmly cemented to the wheel aremerely held by a grease cake or similar substance.[3]Buffing is used to produce a high luster or color without any

particular regard to accuracy of dimension or plane. Cutdown buffing produces a rapid smoothing action with fast-cutting abrasives and relatively hard buffing wheels. It isaccomplished with high speeds and heavy pressures to allowa combined plastic flow and abrading action to occur. Color

buffing is the imparting of a high luster finish on the work piece by use of soft abrasives and soft buffing wheels.

6.3 Lapping

Lapping, like polishing, is an abrading process in whichsmall amounts of material are removed. Unlike polishing,however, lapping is intended to produce very smooth,accurate surfaces, and is never used instead of polishing or

buffing when clearance is the only consideration. Lapping isaccomplished by charging metal forms called laps withflour-fine abrasives and then rubbing the work piece withthe lap. The lap may be of any shape and may be designed tofit into most power machine tools. The only requirements of the lap are that it be of softer material than the material

being lapped, and that it is sufficiently porous to accept theimbedded abrasive grain. Common materials for laps aresoft cast iron, copper, brass, and lead. Some laps are flat and others are cylindrical to fit on steel arbors for internallapping of bores. Cutting oil is recommended for mostlapping operations.

6.4 Polishing and Buffing Speeds

The proper speed for polishing and buffing is governed bythe type of wheel, work piece material, and finish desired.For polishing and buffing in general where the wheels are in

perfect balance and correctly mounted, a speed of approximately 1,750 RPM is used for 6-inch to 8-inchwheels; up to 6-inch wheels use 3,500 RPM. If run at alower rate of speed, the work tends to tear the polishingmaterial from the wheel too readily, and the work is not asgood in quality.

6.5 Polishing Abrasives

The abrasive grains used for polishing must vary incharacteristics for the different operations to which they areapplied. Abrasive grains for polishing are supplied in bulk form and are not mixed with any vehicle. The abrasives,usually aluminum oxide or silicon carbide, range fromcourse to fine (1 to 20 grains per inch).

6.6 Buffing Abrasives

Buffing abrasives are comparatively fine and are often madeup in the form of paste, sticks, or cakes; the abrasive being

bonded together by means of grease or a similar vehicle.The abrasive sizes for buffing are 280, 320, 400, 500, and 600. Some manufacturers use letters and numbers todesignate grain size such as F, 2F, 3F, 4F, and XF (fromfine to very fine). Pumice, rottenstone, and rouge are oftenused as buffing abrasives.

383


3/3



6.7 Lapping Abrasives

Only the finest abrasives are used for lapping. These may beeither natural or artificial. Abrasives for lapping range from

No. 220 to No. 600 or No. 800 which are very fine flours.Lapping compounds are generally mixed with water or oilso that they can be readily applied to the lap.

6.8 Three common uses for grinder

1. Probably the most obvious is grinding.[7] Most anglegrinders are equipped with a 5mm thick metal disk thatare perfect for grinding down just about anything youneed. If you come across some really tough material, youmay need a grinding disc with diamond edges.

2. You can also use your angle grinder for sanding. Thesanding disc usually has rough fiber padding with a

plastic backing. Equipped with this plastic disc, you willhave the perfect sanding tool.

3. The final way you can use your angle grinder is for paintremoval. These circular discs come with pads that are alot softer than the standard angle grinder disc, but this tooldoes an excellent job at removing paint.

7. Weld Dressing and Fitting of MetalFabrication

7.1 Problem

At one ship yard bulk of this work is done with 225 mmelectric high frequency angle grinders. These are largeheavy tools with often have to be held overhead or inawkward position by the operator an average 1 to 3 hours aday. The company has just under 200 of these tools which

product average vibration magnitudes of 7 m/sec 2, given a potential exposure of average of over 4 m/s 2

7.2 Solution

The long term requirement was to use a grinder with bothhigh performance and low vibration. In house engineer reviewed all the grinders available on the market at the timeand decided that a new design of pneumatic 225mm grinder featuring automatic correction for disk unbalance should be

bought initial test should that these new tools using thecompanies usual grinding disk achieved a lower metal

removal rate compared old electric grinders. Further testingrevealed that by changing to as after grade of disc the pneumatic grinders could give a metal removal rate 40%bythe old tool/disc combination.The use of the new tools significantly increased therequirement for compressed air in the shipyard and it wasnecessary to upgrade the air distribution system to cope withthe extra demand.

8. Result

Vibration magnitudes are lower. In extended testing onreal jobs in the yard, the grinders produced an average

vibration magnitude of 3.5m/s2. Efficiency is improved because of the higher rate of

metal removal. The tools are much lighter and so they are easier and less

tiring to operate. There are fewer risks associated with trailing electrical

leads in the working area.

9. Conclusion

The utility grinding machine is intended for offhand grinding where the work piece is supported in the hand and

brought to bear against the rotating grinding abrasive wheel.The accuracy of this type of grinding machine depends onthe operators dexterity. Skill and knowledge of themachines capabilities and the nature of the work. Theutility grinding machine consists of a horizontally mounted motor with a grinding abrasive wheel attached to each end of the motor shaft.

Grinding wheels wear unevenly under most generalgrinding operations due to uneven pressure applied to theface of the wheel when it cuts. Also, when the proper wheelhas not been used for certain operations, the wheel may

become charged with metal particles, or the abrasive grainmay become dull before it is broken loose from the wheel

bond. [n these cases, it is necessary that the wheel bedressed or trued to restore its efficiency and accuracy.

Reference

[1] Adithan, M.; Gupta, A. B. (2002), ManufacturingTechnology , New Age International Publishers, ISBN978-81-224- 0817-1.

[2] T. Saleh, M. Sazedur Rahman, H.S. Lim, M. Rahman,Development and performance evaluation of an ultra

precision ELID grinding machine, Journal of Materials

Processing Technology, Volumes 192-193, Pages 287-291.[3] Stephenson, David. Metal Cutting Theory and

Practice . 2nd. Boca Raton: CRC Press, 1997. 52-60.[4] Salmon, Stuart, "What is Abrasive Machining?,"

Manufacturing Engineering Feb. 2010, Society of Manufacturing Engineers

[5] Benson, Lance Corporal Graham J. (February 26,2009). "Myth busters, Blue Angels come to Yumarange". Marine Corps Air Station Yuma: United StatesMarine Corps. Retrieved 23 May 2010.

[6] Lisbon, Gunnery Sergeant Bill (June 4, 2009). "Myth busters episode filmed in Yuma to air June 10".

MCAS Yuma. Retrieved 23 May 2010.[7] Rochester, Teresa (2009-12-21). "Man killed inaccident T.O. businessman". Ventura County Star.Retrieved 2009-12-29.

Author Profile

Ramesh Kumar is pursuing the M.Tech. (Int.)Mechanical Engineering specialization withProduction Engineering from BhagwantUniversity Ajmer, India

384

Documents

Low-vibration angle grinders